[Ffmpeg-devel] size of encoded file not continous parameter of 'vqscale'

Stefan Gehrer stefan.gehrer
Fri Jun 9 13:19:31 CEST 2006

Darko Veberic wrote:
> hi,
> i am usually encoding video with the following mencoder options:
> -lavcopts vcodec=mpeg4:vqscale=$vq:vhq:v4mv:trell:autoaspect:threads=4
> i have observed strange non-continuous behavior of the resulting file
> size with respect to the vbr quality parameter $vq.
> for example, the file size for vq=4.49 is 911M and for vq=792M (while
> keeping the audio settings constant). i have noticed the jumps occur
> around the x.5 values for the vbr quality... in such cases it is almost
> impossible to get the file size right (ie, close to 700M)...
> is this a bug (or a feature) ?
> best,
vqscale in MPEG4 is whole numbers only (2-31 I believe), and unfortunately
the range of reasonable quality encodes is in the range somewhere like 2 
to 6.
So a step from one vqscale to the next has a huge impact on both quality and
file size. If you need to hit a certain file size, do not use vqscale 
but instead
make use of rate control.

Stefan Gehrer

P.S. I guess this would be better placed at the user mailing list

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